Single-conductor telephone or telegraph



Oct; 15, 1929.

A. B. WATSON SINGLE CONDUCTOR TELEPHONE OR TELEGRAPH Filed Sept. 30, 1921 IN VEN TOR.

A TTORNE Y.

Patented Oct. 15, 1929 SAT S ATE' SINGLE-CONDUCTOR TELEPHONE OR TELEGRAPH Application filed September 30, 1921, Serial No. 504,369.

This invention relates to a system and ap paratus for signaling and more particularly to a system and apparatus for secret telephonic or telegraphic communication.

One of the objects of this invention is to provide a simple and thoroughly practical system and apparatus for secretly signaling between, for example, two 'glVenpoints or stations, and moreover, to provide such a 13 System and apparatus, particularly adaptable for telephonic or telegraphic communication, capable of meeting in a thoroughly practical manner the exacting requirements of secrecy and capable of dependable and reliable operation. Another object is to provide an apparatus which may be readily embodied in durable and rugged, form and which will be of simple arrangement, construction and manipulation. Another object of this invention is to provide an apparatus and system of the above-mentioned nature in which the manifold advantages of utilizing a single conductorfor connecting the two stations may be fully realized in practice while at the same time precluding the possibility of the signals being picked up, by induction or otherwise, excepting where a substantially identical apparatus is directly connected or attached to the single conductor line. Another object is to provide an apparatus of wide range of use and capable of use as a relay between, or for connecting, a single conductor circuit or system having the above-mentioned characteristics and a system or circuit having a complete electrical circuit, such as a two-wire metalllc circuit. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the 49 features of construction, combinations of elements, and arrangements of parts, as will be exemplified in the structure to be hereinafter described and the scope of the appliv cation of which will be indicated in the following claims. p

In the accompanying drawing, in which are illustratedseveral of' possible embodiments of the electrical features of this invention,

Figure 1 is a diagrammatic representation of the apparatus adapted for telephonic communication, and

F igure' 2 is a like diagrammatic representationof the apparatus adapted for telegraphic communication. Similar reference characters refer to simllar parts throughout the several views of the drawing.

Referring now to the drawing and more particularly to Figure 1, it will be noted that the apparatus includes a telephone transmitter 10, which may be of the ordinary carbon granule type, a telephone receiver 26, and a circuit controlling hook 29 arranged to support the telephone receiver 26 when the latter is not in use and arranged further to control certain circuits. Among the circuits controlled by the receiver hook 29 is the circuit of the telephone transmitter 10. The latter is in a circuit which includes the primary winding 12 of a suitable induction coil or transformer, conductor 18, a suitable battery 19, which, by way of example, may be composed'of three ordinary dry cells in series or an ordinary four-volt storage battery, conductor 34, switch contact 31, hook 29 (when urged upwardly by an appropriate spring, as when the receiver 26 is removed from the hook 29),. switch contact 30, conductor 33, and thence back to the telephone transmitter 10. Removal of the receiver 26 from the hook 29 therefore places the local or primary transmitter circuit in .operative condition.

The primary winding 12 of the transformer has associated wlth it an appropriate iron core 11 and a secondary winding 13 inductively related thereto. The circuit of the secondary winding 13 is completed through a condenser 14; the latter may conveniently take the form of a three-plate condenser, as indicated diagrammatically in the drawing, and by way of example may have a capacity of approximately three-tenths of a microfarad. The middle plate of the condenser 14 is connected by way of conductor 21 to the binding post 22 and through the latter connection may be made to the single transmission line conductor L which is-extended to the distant station, where it is connected to the binding post 22 of an apparatus such as that specifically shown in Fi ure 1.

The apparatus thus far descri ed is appropriate for the secret transmission of speech overthe single conductor L, and in action, the sound waves striking the diaphragm of the transmitter 10 cause corresponding variations in the currentv flowing from the battery 19 through the primary coil 12 of the transformer and there is thereby effected the production in the secondary wmding 13 of an alternating E. M. F. varying in frequency and amplitude substantially commensurately with the variations in intensity of the current in the primary circuit caused by the action of the transmitter 10. The circuit of thesecondary winding 13 being vcompleted through the condenser 14, the alternating E. M. F; induced in the secondary winding 13 causes an alternating current to circulate through the thus completed localcircuit and there is made effective across the plates of the condenser 14 analternating E. M. F. substantially commensurate as to frequency and amplitude with the alternating E. M. F. across the secondary 13. The resultant flow of alternating current through the condenser 14 and the resultant stressing of the dielectric between the outside plates of the condenser 1 causes the intermediate plate, to which the'single line conductor L is connected, to partake of variations in potential commensurate as tofrequency, polarity, and amplitude with the alternating E. M. F. across the condenser itself. 3 The single line conductor L will thus be subjected to apotential varying in amplitude at audio or voice frequency and furthermore to a potential which, being an alternating one, is being reversed as to polarity at substantially an audio or voice frequency. During this action, as will be made clear hereinafter, the conductor L, in so far as'the local station is concei'ned, remains ungrounded.

With the understanding that at the distant end of the conductor L there is connected an apparatus similar to that shown in Figure 1,

and adapted upon transmission to affect the potential of'the. conductor L as just hereinabove described, the reception or translation of these potential variations in the conductor L may now be considered. Associated with the apparatus is a thermionic device 15 preferably taking the form of a three-element vacuum tube having a filament cathode 16, a

I grid 20 and a plate 23. The grid 20- is con- 'nected to the conductor 21 and the latter, be-

ing connected to the single line conductor L through the binding post 22, will subject the grid 20 to the potentlal variations impressed upon the line conductor The filament cathode 16 is heated from a suitable source of current, preferably by the battery 19,, and the circuit of the filament 16 is controlled by the switch hook 29. The circuit of the fila-.

.tive, as by the heating of the filament 16, only when the apparatus is in use for reception. The receiver 26 is included in the output circuit of the vacuum tube 15; the latter circuit will be seen to include the plate 23, a battery 24 of appropriate voltage, for example, of forty or forty-five volts, the primary winding 25 of a suitable transformer or induction coil (the purpose of which will be made clear hereinafter), telephone receiver 26, conductor 26, to the filament 16, the circuit being completed by the thermionic path within the vacuum tube and between the filament 16 and the plate 23 thereof. The telephone receiver 26 may be of the usual type and may have a resistance of 2,000 ohms, for example.

Potential variations impressed upon the single line conductor L are likewise, and both as to magnitude and polarity, impressed upon the grid 20 of the vacuum tube 15 and the varying potential of the grid 20 controls with substantially like variations the current flow in the output circuit of the vacuum tube and hence the'current flow through the receiver 26. Where these potential variations take place atan audio or voice frequency rate, the the current flowing through the receiver 26 will be given like variations and the telephone receiver 26 will translate these variations, 1n the usual way, into audible sound variations.

During the receiving action above described, the various parts of the apparatus are in the positions shown in thevdrawing, it

being noted that-the line conductor L re- "'29 takes the position'shown in dotted lines in the drawing. In the latter position, the switch hook 29 engages two switch contacts 38 and 4 0, the latter being connected by conductor 41 to the binding post which is suitabl grounded. Switch contact 38 is connecte by way of conductors 37 and 37 through a normally closed switch 36-associated with the enerator 39 and through the bell 35 to the con uctor 21, which is connected to the line conductor L. The generator 39 is of the manually operated type and the spindle there of is jolnted and arranged so that when the crank is turned, the end of the spindle oppotransformer.

inserting the generator 39 in circuit between the bell 35 and the grounded binding post 42 by Way of conductor 43, conductor 37, switch contact 38, switch hook 29 switch contact 40, conductor 41, and thence to the grounded binding post 42 When, therefore, it is desired to ring or call a distant station, the receiver 26 is left on the hook 29 and the crank of the generator 39 is turned. The current output of the generator then passes through the bell 35 over the single line conductor L, passes through the bell 35 at the distant station to operate the bell, thence by way of switch 36 (closed at the distant station) conductors 37 and 37, switch contact 38, hook 29, contact 40, conductor 41, to the ground by way of grounded binding post 42 (all at the distant station) and returns to the generator at the local station by way of the grounded circuit just traced but in reverse direction.

The distant station having thus been called, telephonic communication in the manner above described, over the single line conductor L butwithout utilization of the ground, may thereupon take place.

Considering such communication to he going on, such communication may be relayed or transmitted over a completed or two-wire circuit in the following manner: The apparatus is provided with two additional binding posts 44 and 48. Binding post 44 is connected by conductor 51 to one terminal of the secondary winding 28 of a transformer or induction coil, the primary winding 25 of which is included in the plate circuit of the vacuum tube 15 and within which circuit is also included telephone receiver 26; a suitable core 27 is interposedbetween the two windings of the transformer. Binding post 48 is connected by way of conductor 5Q, switch 45 and conductor 46 to the other terminal of the secondary winding 28 of the above-mentioned Switch 45 is a two-way switch and may be given the position shown in full lines in the drawing when communication is going on or the position shown in dotted lines, the latter position being utilized only for calling or ringing purposes. In the latter position, conductor 50, and hence binding post 48, is connected by Way of conductor 47 to the conductor 37, the latter being, when the receiver 26 is on the hook 29,

grounded by way of the grounded binding post 42.

Assuming that secret transmission'of intelligence is being carried on over the single conductor L, as hereinabove described, and that it is desired to have the station, considered as including the apparatus shown in Fig 1, act as an intermediary or relay between the channel of secret communication and an ordinary two-conductor signaling channel, the latter has its two conductors connected to the binding posts 44 and 48 and the two conductor circuit will be seen to be inductively related to the circuit including the telephone receiver 26, by way of the transformer 2527-28. Thus, whatever current variations take place in the output circuit of the vacuum tube 15, produced either by the distant station connected over the single conductor L or caused by speaking into the transmitter 10 at the local station (these variations in current in the plate circuit of the vacuum tube 15 being, as will be clear from what has hereinabove been. set forth, under the control of the grid 20, the latter being responsive to the potential variations impressed upon the single conductor L) will be transmitted over the two-conductor line (connected to the binding posts 44 and 48) due to the inductive or transformer coupling 252728. These current variations will thus be transmitted over the two-conductor line and will affect the telephone receiver at the remote end of the latter line in the usual way. On the other hand, should the station at the remote end of the two-conductor line (connected to the binding posts 44 and 48) be transmitting, reception at the local station by way of receiver 26 or reception at the station at the remote end of the single line conductor L by way of the receiver 26 at, that station, may proceed, due to the fact that one of the conductors of the, two-conductor line is connected to binding post 44 and hence, by way of conductor 51, to conductor 21 and therefore to the grid 20 of the vacuum tube 15 at the local station and therefore also through the single line conductorL to the grid 20 of the vacuum tube 15 at the station at the remote end of the single conductor line L; The grids 20 of the two vacuum tubes will therefore be subjected to potential variations characteristic of the conductor connected to the binding post 44, and if these variations are voice or audio frequency variations, these variations will be effective to control with like variations the current flow in' theoutput circuit ofthe vacuum tubes and hence in like manner to affect the telephone receiver 26.

After communication has been concluded, the receiver 26 is, of course, placed upon the hook 29 and the switch 45 given the dotted line position shown in Fig. 1 of the drawing, the apparatus being thereby placed in condition for ringing or calling or being rung or called. The ringing or calling over the single conductor line L has already hereinabove been described, and if the local station desires to ring a station at the remote end of the two-conductor line connected to binding posts 44 and 48, the ringing current generated by the generator 39 will take the following circuit -from generator 39, conductor 43, conductor 47, switch 45 (in its dotted line to be groundedover the following circuit position), conductor 50, binding post 48, through the conductor thereto connected, thence through the bell at the station at the remote end of the two-conductor line, thence through the conductor connected to binding post 44. conductor 51, conductor 21, bell 35, and back to the generator 39. Thus the generator 39 may ring the station connected to the binding posts 44 and 48 and. at the same time may ring thestation connected to the remote end of a line L in the manner hereinbefore described.

Should the station connected to the binding posts 44 and 48 over a two-conductor line desire to ring a local station, the ringing current may be considercd as coming over the line connected to the binding post 44, passing thence through conductor 51, conductor 21, the bell 35, switch 36 (in closed position, since the crank of generator 39 is at rest), conductor 37 conductor 43, conductor 47, switch 45 (in its dotted line position), conductor 50, binding post 48-. and thence back to the remote station, over the line connected to the latter binding post. Thus the local station is signaled by thus causing bells 35 to be operated. At the same time, however, the station at the remote end of the single conductor line L is signaled inasmuch as the bell 35 at the remote station is connected in parallel with the bell 35 at the local station; this will be clear since one terminal of the bell 35 at the distant station is connected to the line L in the same manner as the bell 35 of the local station is connected to the binding post 22 and hence to the line L. The other terminal of the bell 35 at the local stat-ion will be seen switch 36 (in closed position), conductor 37 conductor 37, switch contact 38, book 29 (in itslower dotted line position), switch contact 40, conductor 41, and thence to ground by way ofa grounded binding post 42. The

remaining terminal of the bell35 at the station at the remote end of the single conductor line L will be grounded in a manner similar to that just described with respect to the bell 35 at the local station Whatever potential therefore that is applied to the bell 35 at .the local station for operating the local calling bell will be applied (leaving out of consideration line losses) to the bell atthe remote end of the single conductor line L.

It will similarly be clear that the operation of the calling generator at the station at the remote end of the singleconductor line'L will operatenot only the bell 35 at the local station but also the bell at the station connected to the binding posts 44 and 48, since the bells at the'ftwo latter stations will be connected in parallel over the two line conductors con- .nected to the binding posts 44 and 48. Thus the calling or ringing of one station by any of the others, even assuming that the apparatus forming part of. my invention acts as an If it is desired to carry on telegraphic communication instead of telephonic communication as hereinbefore described, the transmit ter 10 of Fig. 1' is replaced by a buzzer or dircct current interrupter diagrammatically indicated at 52 in Fig. 2 and by'a telegraph key 53 connected in series therewith. The operation and action of the apparatus for telegraphic communication will be substantially the same as hereinbefore described with respect to telephonic communication, it being noted that instead of utilizing the energy of the vibrations set up bythe voice for varying, by way ofa transmitter such as the transmitter 10, the current in the primary circuit of the transformer or induction coil 12-13, the buzzer acts to interrupt or vary the current in this same primary circuit at an appropriate audio rate. the operation of the buzzer being in turn controlled by the telegraph key to produce the appropriate telegraphic dot and dash signals.

It will thus be seen that there has been provided' in this invention a system and apparatus in which the objects of thisinvention,

.together' with many thoroughly practical advantages are successfully achieved. It will be seen that, in so far as concerns the two stations connected 'at the'spaced ends of the single conductor L, the only use made of the ground as a'conductor' is for purposes of calling or ringing of one station by the other, and that when telephonic or telegraphic communication is carried on between such two stations use is made only of the single conductor line L alone the potential of which is varied or changed by theme station and the other station being adapted to respond simply to these potential variations or changes and being operative withouthaving to depend upon current flow through the single line conductor L itself. The picking up of the messages sent over the single. line conductor L- either by induction or leakage of current therefrom,

as is possible with the usual systems 'ofcom munication, is thus effectively precluded.

As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim as myinvention:

1. A transmitter for impressing upon a single line conductor variations in its .electrical condition combined with a receiver therefor, comprising, in combination, a source of unidirectional E. M. F., a condenser adapted to have said line conductor connected to a plate thereof, means for converting said unidirectional E. M. F. into an alternating E. M. F., the circuit of said last-mentioned .means being completed through said condenser, a thermionic device having a filament electrode supplied with heating current from said source of unidirectional E. M. F. and having another electrode adapted to have said l ine conductor connected thereto, a telephone receiver controlled by said thermionic device, a switch hook for receiving said telephone receiver, and means controlled by said hook for controlling the flow of current from said source of unidirectional E. M. F. to said converting means and to said filament.

2. In a system for electrical signaling, in combination, a line conductor connecting two stations, signaling means at one station for im ressing upon said conductor variations in its electrical potential free from detectable displacement current flow through said conductor, and translating means at the other station responsive to said electrical potential variations in said line conductor. i

3. In a system for electrical signaling, in combination, a line conductor connecting two stations, signaling means at one station for impressing upon said conductor variations in its electrical potential free from detectable displacement current flow through said conductor, a thermionic device at the other station having an electrode thereof connected to said line conductor to be responsive to the potential variations'in the latter, and translating means controlled by said thermionic device.

4. In a system for electrical signaling, in combination, a line conductor for connecting two stations,- and signaling means at one station for impressing upon said conductor variations in its electrical condition, said means including a local energizing circuit at said one station having included therein a condenser, said line conductor being connected to a plate of said condenser.

5. In a system for electrical signaling, in combination, a line conductor for connecting two stations, signaling means. at one station for impressing upon said conductor variations in its electrical condition, said means including a source of alternating E. M. F. adapted to be ailected'in accordance with'the signals desired to be transmitted, and a condenser for completing the local circuit of said source of alternating E. M. F., said line conductor being connected to a plate of said condenser. v

6. In a system for electrical signaling, in

plates and aplate intermediate of said opposed plates, said intermediate plate being connected to said conductor.

7 In a system for electrical signaling, in

combination, a line conductor connecting two stations, signaling means at one station for impressing upon said conductor variations in its electrical condition, said means including a source of alternating E. M. F. adapted to be affected in accordance with the signals desired to be transmitted, and means adapted to complete the circuit of said source of al .ternating E. M. F. and to form a local circuit therefor, said last-mentioned means having a plurality of terminals between which is effective an alternating potential difference, said line conductor being connected to one of said terminals.

8. In a system for electrical signaling, in combination, a line conductor connecting two stations; signaling means at one station for impressing upon said conductor variations in its electrical condition, said means includin a source of potential adapted to be affecte in accordance with the signals desired to be transmitted, and means adapted to complete locally the circuit of said source of potential to form a local circuit therefor, said last-mentioned means having a plurality of terminals between which is efiective a signaling potential difierence, said line conductor being connected to one of said terminals, an electronic device having a control element connected to be responsive to variations in the electrical condition of said line conductor and having an electrode to which is connected an output circuit, a translating device connected in said output circuit; means for coupling said output circuit to another channel ofcommunication; a source of calling current; and means for making said source of calling current effective upon both said line conductor and said other channel of communication and operative during ineffectiveness of said signaling means.

9/A. signaling apparatus comprising, in combination, signal transmitting means for impressing upon a single line conductor variations in its electrical condition, a. telephone receiver, means responsive to variations-in the electrical condition of said single line conductor when impressed thereon by a distant station for controlling the current flow through said telephone receiver, a ground connection, a source of calling E. M. F. adapt ed to have one terminal connectedto said single line conductor, a hook for holding said telephone receiver and arranged, when the receiver is on the hook, to connectthe other combination, signal transmitting means for impressing upon a single line conductor variations in its electrical condition,'a telephone receiver, meansresponsive to variations in the electrical condition of said single line conductor when impressed thereon by a distant station for controlling the ci'irrent fiow through said telephone receiver, a ground connection,a source of calling E. M. F. adapted tohave one terminal connected to said single line conductor, a hook for holding said telephone receiver and arranged, when the receiver is on the hook, to connect the other terminal of said source of calling E. M. F. to said ground connection, and, when said receiver is off the hook, to make operative said signal transmitting means and to free the apparatus irom said ground connection.

11 A signaling apparatus comprising, in combination, signal transmitting means for impressing upon a single line conductor variations in its electrical condition, a telephone receiver, means responsive to variations in the electrical condition, of said single line conductor when impressed thereon by a distant station for controlling the current flow through said telephone receiver, a ground connection, a source of calling E. M. F. adapted to have one terminal connected to said single line conductor, a hook for holding saidtelephone receiver and arranged, when the receiver is on the hook, to connect the other terminal of--said source of calling E. M. F. to said ground connection, and, when said receiver isoii the hook, to make operative said signal-responsive means and to tree the apparatus from said ground connection.

I 12. A signaling station adapted to be connected to a distant station by a single line conductor free from a grounded return and to be connected to a second dis- .tant station over a line conductor with rethermionic device and the other winding of. which has its one terminal connected to theline' conductor leading to said second-mentioned distant station and its other terminal connected to the return circuit from said second-mentioned distant station, whereby current variations commensurate with the potential variations impressed upon the single conductor line leading to said first-mentioned distant station may be transmitted to said second-mentioned distant station,

13. A signaling station adapted to be conconductor extending to said first-mentioned distant station being connected to one of said terminals, thereby to have impressed thereon potential variations, a transformer, the secondary Winding of which has its one terminal connected to the-line conductor leading to said second-mentioned distant station and the other terminal of which is connected to the return circuit from said second-mentioned station, and means for aifecting the primary winding of said transformer by a function of said alternating E. M. F. whereby current variations commensurate with the potential variations impressed upon said first-mentioned single line conductor may be transmitted to said second-mentioned distant station over said second-mentioned line conductor with its associated return circuit.

14. A receiving station adapted to be conneoted to a distant station by a single conductnr line free fronra return circuit and adapted to be connected to a second distant station tial variations, a transformer, one winding of which is connected in the plate circuit and the other winding of which has its one terminal connected to the line conductor leading to said second-mentioned distant station and its other conductor connected to the return circuit leading to said second-mentioned distant station, whereby signaling current variations transmitted to said last-mentioned winding from said second-mentioned distant station are made efiective to vary the current flow in the late circuit of said thermionic device and t us to affect said translating device.

15. A relay signaling station adapted to interconnect a two-conductor channel of communication with a single conductor channel of communication free from a return circuit, comprising, in combination, a three-element thermionic device having its grid arranged to be responsive to potential variations inip ressed upon said single conductor channel of communication and having included in its plate circuit one winding of a transformer, the other Winding of which has connected to its terminals said two-wire channel of communication leading to said first-mentioned distant station.

16. A signaling apparatus adapted for communication with and interconnection between a single conductor line leading to a distant station and free from a return ,circuit and a two-conductor channel of communication leading to a second distant station, comprising, in combination, signaling means for impressing upon said single lineconductor variations in its electrical potential, :1 three-element thermionic device having its grid connected to be responsive to potential variations in said single line conductor and impressed thereon by a distant station and connected also to be responsive to potential variations in one of the conductors of said two-conductor channel of communication leading to said second-mentioned distant station, a translating device in the output circuit of said thermionic device and adapted thereb to translate signaling variations impresse upon said grid by either of said channels of communication, and a transformer having its one winding connected in the output circuit of said thermionic device and having its other winding connected to said two-conductor channel of communication, whereby current variations commensurate with the potential variations impressed upon said single line conductor are transmitted to said other distant station over the two-conductor line connected thereto.

17 In a system for electrical signaling, in combination, a line conductor for connecting two stations, signaling means at one station for impressing upon said conductor variations in its electrical condition, said means including a source of alternating E. M. F. adapted to be affected in accordance with the signals desired to be transmitted, a condenser for completing locally the circuit of said source of alternating E. M. F., said line conductor being connected to a plate of said condenser, an electronic device having included therein a control element and an electrode, said control element being connected to said line conductor, and an output circuit for said electronic device having included therein a translating device and a coupling device to which may be connected the conductor or conductors of another channel of con'imunication.

18. In a system for electrical signaling, in combination, a line conductor connecting two stations; signaling means at one station for impressing upon said conductor variations in its electrical condition, said means the electrical condition of said line conductor and having an electrode to which is connected an output circuit; and means for coupling said output circuit to another channel of communication.

19. In a system for electrical signaling, in combination, a line conductor connecting two stations; signaling means at one station for impressing upon said conductor varia tions in its electrical conditions, said means including a source of potential adapted to be affected in accordance with the signals desired to be transmitted, and means adapted to complete locally the circuit of said source of potential to form a local circuit therefor, said last-mentioned means having a plurality of terminals between which is effective a signaling potential difference, said line conductor being connected to one of said terminals, an electronic device having a control element connected to be responsive to variations in the electrical condition of said line conductor and having an electrode to which is connected an output circuit, a translating device included in said output circuit; and means for coupling said output circuit to another channel of communication.

ALDWYN B. WATSON. 

